call super().__init_subclass__(); support GenericAlias

Improved the :class:`.DeclarativeBase` class so that when combined with
other mixins like :class:`.MappedAsDataclass`, the order of the classes may
be in either order.

Added support for mapped classes that are also ``Generic`` subclasses,
to be specified as a ``GenericAlias`` object (e.g. ``MyClass[str]``)
within statements and calls to :func:`_sa.inspect`.

Fixes: #8665
Change-Id: I03063a28b0438a44b9e028fd9d45e8ce08bd18c4

2 files changed, 14 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/decl_api.py b/lib/sqlalchemy/orm/decl_api.py
index 5724d53a2..a43b59a45 100644
--- a/lib/sqlalchemy/orm/decl_api.py
+++ b/lib/sqlalchemy/orm/decl_api.py
@@ -581,7 +581,6 @@ class MappedAsDataclass(metaclass=DCTransformDeclarative):
         match_args: Union[_NoArg, bool] = _NoArg.NO_ARG,
         kw_only: Union[_NoArg, bool] = _NoArg.NO_ARG,
     ) -> None:
-
         apply_dc_transforms: _DataclassArguments = {
             "init": init,
             "repr": repr,
@@ -696,6 +695,7 @@ class DeclarativeBase(
             _setup_declarative_base(cls)
         else:
             _as_declarative(cls._sa_registry, cls, cls.__dict__)
+        super().__init_subclass__()
 
 
 def _check_not_declarative(cls: Type[Any], base: Type[Any]) -> None:
diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 0f16df9c8..b9d1b50e7 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -79,6 +79,7 @@ from ..util.langhelpers import MemoizedSlots
 from ..util.typing import de_stringify_annotation
 from ..util.typing import is_origin_of_cls
 from ..util.typing import Literal
+from ..util.typing import typing_get_origin
 
 if typing.TYPE_CHECKING:
     from ._typing import _EntityType
@@ -1361,6 +1362,18 @@ def _inspect_mc(
         return mapper
 
 
+GenericAlias = type(List[_T])
+
+
+@inspection._inspects(GenericAlias)
+def _inspect_generic_alias(
+    class_: Type[_O],
+) -> Optional[Mapper[_O]]:
+
+    origin = cast("Type[_O]", typing_get_origin(class_))
+    return _inspect_mc(origin)
+
+
 @inspection._self_inspects
 class Bundle(
     ORMColumnsClauseRole[_T],